Microwave apparatus and methods of performing chemical reactions

ABSTRACT

The present invention relates to an apparatus and methods for performing chemical reactions. In particular, the present invention relates to an apparatus for heating chemical reaction mixtures. The apparatus applies one or more semiconductor based microwave generators making the apparatus suitable for parallel processing of chemical reaction mixtures. The invention further relates to methods for performing chemical reactions, e.g. methods for heating a plurality of samples simultaneously or sequentially, methods for monitoring a microwave heated chemical reaction, and methods where the optimum conditions with respect to parameters, such frequency and applied power can be determined for the system consisting of apparatus plus sample.

[0001] The present invention relates to an apparatus for heatingchemical reaction mixtures. In particular, the present invention relatesto an apparatus applying one or more semiconductor based microwavegenerators making the apparatus suitable for parallel processing ofchemical reaction mixtures. The invention further relates to methods forperforming chemical reactions, e.g. methods for heating a plurality ofsamples simultaneously or sequentially, methods for monitoring amicrowave heated chemical reaction and methods where the optimumconditions with respect to frequency and applied power can bedetermined.

[0002] One of the major obstacles for an organic chemist today is thetime consuming search for efficient routes in organic synthesis. As anexample, the average performance some ten years ago in thepharmaceutical industry was around 25-50 complete substances per chemistper year resulting in an equal amount of new chemical entities aspotential new drug candidates. Today the figure is several 100's peryear and will soon be expected to be in the region of 1000's per year.

[0003] Thus, the challenges for the pharmaceutical industries and theorganic chemist include identification of ways of reducing time in drugdevelopment, identification of ways of creating chemical diversity,development of new synthesis routes and maybe reintroduction of old“impossible” synthetic routes. Also, it is a constant challenge to reachclasses of totally new chemical entities.

[0004] As it will be apparent from the following, microwaves assistedchemistry offers a way to circumvent at least some of theabove-mentioned problems, namely

[0005] speeding up the reaction time with several orders of magnitudes,

[0006] improving the yield of chemical reactions,

[0007] offering higher purity of the resulting product due to rapidheating and thereby avoiding impurities from side reactions, and

[0008] performing reactions which are not possible with conventionalthermal heating techniques.

[0009] Microwave assisted chemistry has been used for many years.However, the apparatuses and methods have to a great extent been basedon conventional domestic microwave ovens. Domestic microwave ovens havea multimode cavity and the energy is applied at a fixed frequency at 915MHz or 2450 MHz (depending on country). The use of single mode cavitieshave also been reported, see e.g., U.S. Pat. Nos. 5,393,492 and4,681,740.

[0010] The market for microwave generators is totally dominated bymagnetrons. In some situations travelling wave tubes (TWT) are used toamplify a microwave signal. There are several disadvantages related tothe conventional apparatuses. Some of these will be listed in thefollowing:

[0011] It is a disadvantage that the energy distribution in conventionalmicrowave ovens is non-uniform. This leads to a varying temperature inthe sample depending on the position of the sample in the oven.Furthermore, the non-uniform energy distribution makes it difficult toobtain reproducible results. This effect is especially noticeable if anarray of sample holders such as a microtiter plate (e.g. with 96 wells)is used. Rotation of the sample in the oven does not significantlyimprove the reproducibility.

[0012] In conventional systems the power provided to each sample in anarray of samples can only be calculate as an average power per sample bydividing the measured input power with the total number of samples. Dueto the non-uniform energy distribution in the cavity this calculationwill only provide a rough estimate of the applied power to each sample.

[0013] One way of controlling the reaction is to monitor pressure andtemperature in all individual wells. This may give information of theconditions in a specified well during a particular run. Changing theposition will give a different result leading to poor reproducibility.An alternative way of trying to obtain a uniform energy distribution isto place a large load in the cavity in order to absorb energy moreuniformly.

[0014] Single mode cavity resonators offer a possibility of highefficiency and controlled heating patterns in small loads. However, thedielectric properties of the load often change considerably withtemperature, resulting in very large variations in power absorptionsince an essentially constant frequency microwave generator is used.Hence, the process becomes difficult to predict.

[0015] A further disadvantage of conventional system relates to the factthat magnetrons usually only provide a fixed frequency or a minoradjustment around the centre frequency of the magnetron. Furthermore,magnetrons have an unpredictable behaviour and are extremely temperaturesensitive, especially when the efficiency decreases, towards the end ofits “life”.

[0016] TWT's have be used as variable frequency amplifiers.However,TWT's are rather expensive and often very complicated to use.Furthermore,TWT's require warm-up time before start meaning that TWT'scannot rapidly be switched on and off. In addition, wear out ofTWT's isassociated with high maintenance costs.

[0017] Both magnetrons and TWT's require a high voltage power supply,which is a disadvantage in view of complications and the risk.

[0018] In U.S. Pat. No. 5,521,360 a variable frequency heating apparatusfor providing microwaves into a furnace cavity is described. Theapparatus comprises a voltage controlled microwave generator, a voltagecontrolled pre-amplifier and a power amplifier. The power amplifier maybe a TWT. The TWT is operationally connected to the furnace cavity. Thepower delivered to the furnace is determined by measuring the powerreflected from the furnace using a power meter. Upon placing a sample inthe cavity furnace, power may be coupled to the sample causing thetemperature of the sample to change.

[0019] The system described in U.S. Pat. No. 5,521,360 suffers from theabove-mentioned disadvantages relating to e.g. TWT's.

[0020] It is a further disadvantage of the apparatus described in U.S.Pat. No. 5,521,360 that it is restricted to be used with only one cavityfurnace, i.e. parallel heating of a plurality of samples using differentheating parameters is not possible.

[0021] It is another object of the present invention to provide anapparatus comprising a first semiconductor based electromagneticgenerator, and a first applicator for holding a sample, which apparatusare capable of performing a controlled heating of the sample.

[0022] It is another object of the present invention to provide anapparatus capable of performing parallel processing of many samples,with individually settings of process parameters such as frequency,power, temperature, pressure etc.

[0023] It is a further object of the present invention to provide anapparatus capable of monitoring many samples in parallel, withindividually monitoring of process parameters such as frequency, power,temperature, pressure etc.

[0024] It is a still further object of the present invention to providean apparatus capable of controlling many samples in parallel, withindividually adjustments of process parameters such as frequency, power,temperature, pressure etc.

[0025] It is a still further object of the present invention to providean apparatus in which samples can be evenly heated by using variousapplicators.

[0026] It is a still further object of the present invention to providean apparatus in which the frequency of the applied energy can be varied.

[0027] It is a still further object of the present invention to providean apparatus in which it is possible to evaluate and separate thermaland chemical effects on the electromagnetic absorption capability andbehaviour of the sample.

[0028] It is a still further object of the present invention to providean apparatus in which it is possible to measure the temperature in thereaction vessel by monitoring the change in resonance frequency of asecond material introduced into the reaction chamber. This materialcould be a crystal, semiconductor or any other solid state material witha temperature dependent resonance frequency.

[0029] The above-mentioned objects are complied with by providing in afirst aspect an apparatus for providing electromagnetic radiation to afirst applicator, said apparatus comprising:

[0030] a) a first generating means for generating electromagneticradiation,

[0031] b) a first amplifying means for amplifying the generatedelectromagnetic radiation,

[0032] c) means for guiding the amplified electromagnetic radiation tothe first applicator, and

[0033] d) means for controlling the first generating means and the firstamplifying means,

[0034] wherein the generated electromagnetic radiation comprises aplurality of frequencies, and wherein the first generating means and thefirst amplifying means are essentially constituted by semiconductorcomponents.

[0035] By essentially constituted by semiconductor components is meantthat the components generating the electromagnetic radiation—such as therequired power transistors—are semiconductor based power transistors.

[0036] In the present context, guiding means should be interpreted asany means capable of guiding electromagnetic radiation such as metallicchannels or cables, such as coaxial cables or waveguides. The guidingmeans may also comprise active and/or passive components such ascouplers, dividers, splitters, combiners, isolators, power meters,artificial loads, spectrum analysers etc.

[0037] In order to perform parallel processing of a plurality samplesthe apparatus may comprise a second applicator and suitable guidingmeans for guiding at least part of the amplified electromagneticradiation to the second applicator. Generally it may be favourable to beable to provide electromagnetic radiation with different frequencies tothe first and second applicator. Therefore, the apparatus may comprise asecond generating means for generating electromagnetic radiation at aplurality of frequencies and a second amplifying means for amplifyingthe electromagnetic radiation generated by the second generating means.In order to provide electromagnetic radiation at a plurality offrequencies the second generating means and the second amplifying meansare preferably constituted by semiconductor components, such assemiconductor based power transistors. Examples of such powertransistors are silicon-carbide power transistors. It is evident thatthe same type of transistors may be used in first generating means andthe first amplifying means.

[0038] To increase flexibility of the apparatus, the guiding means maycomprise means for guiding the electromagnetic radiation amplified bythe second amplifying means to the second applicator. In addition, theguiding means may further comprise means for guiding at least part ofthe electromagnetic radiation amplified by the second amplifying meansto the first applicator.

[0039] Also, in order to further increase flexibility of the apparatusthe guiding means may comprise means for switching the electromagneticradiation amplified by the first amplifying means between the first andsecond applicator. Furthermore, the guiding means may comprise means forswitching the electromagnetic radiation amplified by the secondamplifying means between the first and second applicator.

[0040] The first and second applicators may be of various types.Preferable, the first and second applicators are selected from the groupconsisting of quasistatic, near field, surface field, single mode cavityand multi mode cavity applicators.

[0041] The frequency of the electromagnetic radiation generated by thefirst and second generating means may vary according to a first andsecond control signal, respectively. These first and second controlsignals may be provided by the control means. Similarly, theamplification of the first and second amplifying means may vary inaccordance with a first and a second control signal, respectively. Alsothese signals may be provided by the control means. The control meansmay comprise a general purpose computer. Such a general purpose computermay form part of a neural network.

[0042] The frequency of the electromagnetic radiation generated by thefirst and second generating means is within the range 300 MHz-300 GHz,such as within the range 0.5-3 GHz or within the range 50-100 GHz.

[0043] In a second aspect, the present invention relates to a method forperforming a plurality of chemical reactions simultaneously orsequentially, said method comprising the steps of:

[0044] a) providing a first sample into a first applicator,

[0045] b) providing a second sample into a second applicator, and

[0046] c) applying electromagnetic radiation to the first and secondsamples simultaneously or sequentially for a predetermined period oftime, said electromagnetic radiation having a frequency in the range of300 MHz-300 GHz.

[0047] The electromagnetic radiation may be provided specifically andindependently to each of the samples. In addition, the appliedelectromagnetic radiation may comprise one or more pulses. The samplesmay be collected in sets comprising at least two holders. The sampleitself may be a PCR mixture. During exposure of a sample theelectromagnetic radiation may be applied in cycles of at least two stepswhere the sample is cooled at least during part of each cycle.

[0048] Preferably, the electromagnetic radiation is provided using anapparatus according to the first aspect of the present invention.

[0049] In a third aspect, the present invention relates to a method forperforming a chemical reaction, said method comprising the steps of:

[0050] a) providing a sample in an applicator,

[0051] b) applying electromagnetic radiation to the sample for a firstpredetermined period of time at a first level of power and varying thefrequency of the electromagnetic radiation between two predeterminedvalues and with a predetermined resolution, and determining a reflectionfactor of electromagnetic radiation from the sample at at least some(two) of the frequencies covered by the range of the two predeterminedvalues by determining the level of a feed-back signal, thereby obtaininga first set of reflection factors,

[0052] c) changing the physical and/or chemical properties of thesample,

[0053] d) applying electromagnetic radiation to the applicator at asecond level of power and varying the frequency of the electromagneticradiation between two predetermined values and with a predeterminedresolution, the range defined by the predetermined values being includedin the range defined by the predetermined values in step b), anddetermining a reflection factor of electromagnetic radiation from thesample at at least some (two) of the frequencies covered by the range ofthe two predetermined values by determining the level of the feed-backsignal, thereby obtaining a second set of reflection factors, and

[0054] e) repeating step c) and d) until the difference in reflectionfactors calculated as the mathematical difference (subtraction) betweenthe frequencies associated with the first and second set of reflectionfactors is within a predetermined range.

[0055] Step c) may comprise applying electromagnetic radiation forheating the sample. Alternatively or in addition, the sample may also becooled and/or a reagent may be added to the sample. Also, if thedifference in reflection factors is within the predetermined range afterthe first execution of step c) and d), step e) will off course no longerapply. Furthermore, if the difference is close to being within thepredetermined range, it might not be economical to perform step e), andit may be omitted.

[0056] In a fourth aspect, the present invention relates to a method forperforming a chemical reaction, said method comprising the steps of:

[0057] a) providing a sample in an applicator,

[0058] b) applying electromagnetic radiation to the sample, theelectromagnetic radiation having a starting frequency,

[0059] c) varying the frequency of the applied electromagnetic radiationbetween two predetermined values and with a predetermined resolution,

[0060] d) determining a reflection factor of electromagnetic radiationfrom the sample by determining a level of a feed-back signal during atleast part of the varying of the frequency of the electromagneticradiation, and

[0061] e) determining, from the level of the feed-back signal, thefrequency of the electromagnetic radiation where the reflection factoris within a predetermined range.

[0062] In a fifth aspect, the present invention relates to a method forperforming a chemical reaction, said method comprising the steps of:

[0063] a) providing a sample in an applicator,

[0064] b) applying electromagnetic radiation to the sample, theelectromagnetic radiation having a starting frequency,

[0065] c) varying the frequency of the electromagnetic radiationincrementally around the starting frequency,

[0066] d) determining a reflection factor of electromagnetic radiationfrom the sample by determining a level of a feed-back signal at thestarting frequency, at a frequency incrementally lower than the startingfrequency and at a frequency incrementally higher than the startingfrequency,

[0067] e) repeating step b) to d) until the reflection factor isminimum.

[0068] In a sixth aspect, the present invention relates to a method forperforming a chemical reaction, said method comprising the steps of:

[0069] a) providing a sample in an applicator,

[0070] b) applying electromagnetic radiation to the sample, theelectromagnetic radiation having a starting frequency,

[0071] c) varying the frequency of the electromagnetic radiationincrementally around the starting frequency,

[0072] d) determining a reflection factor of electromagnetic radiationfrom the sample by determining a level of a feed-back signal at thestarting frequency, at a frequency incrementally lower than the startingfrequency and a frequency incrementally higher than the startingfrequency,

[0073] e) comparing the determined reflection factor with apredetermined reflection factor,

[0074] f) adjusting the starting frequency to a frequency so that thedetermined reflection factor is within a predetermined range around thepredetermined reflection factor, and

[0075] g) repeating step c) to f) as often as desirable

[0076] The starting frequency may be in the range of 300 MHz-300 GHz.The predetermined values between which the frequency of the,electromagnetic radiation may be varied are in the range of 300 MHz-300GHz, such as within the range 0.5-3 GHz or within the range 50-100 GHz.Preferably, the reactions according the third, fourth, fifth and sixthare performed using an apparatus according to first aspect of thepresent invention.

[0077] In a seventh aspect, the present invention relates to a methodfor performing a chemical reaction, said method comprising the steps of:

[0078] a) providing a sample in an applicator,

[0079] b) applying electromagnetic radiation to the sample in form of afirst pulse with a predetermined shape and characterising a reflectedpulse from the applicator by performing a mathematical operation so asto obtain a first reflected spectrum,

[0080] c) changing the physical and/or chemical properties of thesample,

[0081] d) applying electromagnetic radiation to the sample in form of asecond pulse with a predetermined shape and characterising a reflectedpulse from the applicator by performing a mathematical operation so asto obtain a second reflected spectrum,

[0082] e) repeating step c) and d) until the difference between thefirst and second reflected spectra calculated as the mathematicaldifference (subtraction) between the first and second spectra is withina predetermined range.

[0083] If the difference in reflection factors is within thepredetermined range after the first execution of step c) and d), step e)will off course no longer apply. Furthermore, if the difference is closeto being within the predetermined range, it might not be economical toperform step e), and it may be omitted. Preferably, the mathematicaloperation for obtaining the first and second reflection spectracomprises Fourier Transformation but alternative operations may also beapplicable. The method according to the seventh aspect of the presentinvention may be performed using an apparatus according the first aspectof the present invention.

[0084] In a eight aspect, the present invention relates to the use of anapparatus according to the first aspect of the present invention forheating at least one sample comprising at least one organic compound.Each of the samples may further comprise one or more reagents andoptionally a catalyst. Preferable, the apparatus according the firstaspect of the present invention is configured to heat two or morereaction mixtures, such as PCR mixtures, simultaneously or sequentiallyor intermittently.

[0085] The frequency of the electromagnetic radiation, the level ofirradiated power and the period of applying the electromagneticradiation is determined by pre-set values for the chemical reaction inquestion, such pre-set values being stored in a storage means associatedwith the control means. Corresponding data of frequency and reflectionfactor may be stored in a memory for further processing. Furtherprocessing may be performed in a neural network.

[0086] In a ninth aspect, the present invention relates to a kit forchemically reacting chemical species with a reagent optionally under theaction of a catalyst, wherein the chemical reaction is performed in anapparatus according to the first aspect of the present invention, saidkit comprising:

[0087] a) a sample holder comprising at least one of the reagent and theoptional catalyst,

[0088] b) an electronic storage means comprising data concerning thechemical reaction between the chemical species and the reagent under theoptional action of the catalyst, said electronic storage means andapparatus being adapted for retrieving the data from the storage meansand processing said data so as to control the application of anelectromagnetic radiation to said sample holder.

[0089] This aspect may further comprise instructions regarding additionof the chemical species to the sample holder.

[0090]FIG. 1 illustrates possible combinations of the three main modulesin an apparatus according to the invention.

[0091]FIG. 2 illustrates an embodiment comprising of the apparatusaccording to the present invention.

[0092]FIG. 3 illustrates an applicator mounted in a microtiter plate.

[0093]FIG. 4 illustrates a microtiter plate with a microwave conductormounted symmetrical in the centre of four wells.

[0094]FIG. 5 illustrates a microtiter plate with transmitting typeapplicator with input and output parts 12 and 13.

[0095]FIG. 6 illustrates a microtiter plate with an individual antennafor each sample well.

[0096] As mentioned above, the present invention provides an apparatusand methods for performing chemical reactions, preferably chemicalreactions performed in parallel. A particular interesting feature of theapparatus according to the invention is the use of semiconductorcomponents in the signal generator and amplification means. As will beclear from the following, the semiconductor signal generator offershitherto unrealised advantages in chemical synthesis and thus also inthe methods according to the invention.

[0097] The main purpose of utilising microwaves or other electromagneticradiation in an apparatus and methods for performing chemical reactionsis to heat and/or catalyse reactions taking place in a sample exposed tomicrowave radiation. Preferably the sample is placed in a sample holderin the applicator of the apparatus.

[0098] Also, according to the apparatus and the method according to thepresent invention, the signal generator can be controlled in response tothe actual level of signal energy supplied to—and/or absorbed in—theapplicator. This feedback makes it feasible to control e.g. thetemperature of the samples to a very high degree.

[0099] The term microwave is intended to mean electromagnetic radiationin the frequency range 300 MHz-300 GHz. Preferably, the apparatus andmethods according to the invention are performed within the frequencyrange of 500 MHz-300 GHz, preferably within the frequency range 500MHz-30 GHz such as 500 MHz-10 GHz such as 2-30 GHz such as 300 MHz—4 GHzsuch as 2-20 GHz such as 0.5-3 GHz or within the range 50-100 GHz.

[0100]FIG. 1 illustrates a preferred embodiment of an apparatusaccording to the present invention. The number n of signal generators 28that are separately amplified by signal amplifiers 29 are connected tothe number m of separate applicators 24 through the distributing network23, represented by the box in the centre. It is seen that all componentsare connected to the power supply 44 and the controller 45. FIG. 1illustrates parallel processing of samples, and that generators andapplicators are preferably controlled in response to the coupling ofmicrowave energy in the distributing network, the applicator or thesample. It should be mentioned that each applicator 24 can contain oneor more samples.

[0101] If the average power to be delivered to each applicator 24 isless than the maximum output power of an amplifier 29, the number ofapplicators 24 can exceed the number of generators 28 and amplifiers 29,hence n<m. If the average power to be delivered to each applicator 24 islarger than the maximum output power of an amplifier 29, the power foreach applicator can originate from several amplifiers. Hence the poweroutput from some amplifiers can be distributed to several differentapplicators. In this case the number of applicators 24 can be less thanthe number of generators 28 and amplifiers 29, hence n>m. This guidingand coupling of radiation between amplifiers and applicators isperformed by the distributing network 23. Each amplifier and applicatorcan also be coupled in pairs, that is n=m.

[0102] In the following, the individual components comprised in theapparatus will be described in more detail, including some preferredfeatures.

[0103] The generating means 28 and the amplifying means 29 areessentially constituted by semiconductor components. in order to be ableto generate a signal between 300 MHz and 300 GHz, several individualsemiconductor based generators may be needed.

[0104] The power of the generated signal varies continuously between 0and 1 W. The signal generator is capable of driving a signal amplifierand/or a power amplifier. Furthermore the signal generator iscontrollable/programmable from the controller 45. The control functionsis in the form of controlling the amplitude, frequency, frequencybandwidth, signal form, pulse form or duration of the signal/pulse andany combinations of two or more functions at the same time.

[0105] Semiconductor based microwave generators and amplifiers providesa variety of advantages over conventional TWT's, gyrotrons andmagnetrons. Examples of these advantages are:

[0106] Easy control of frequency and output power

[0107] Small physical dimensions

[0108] No high voltage required, which improves safety and reliability

[0109] No warm-up time, therefore immediately availability

[0110] No wear-out parts which significantly reduce cost maintenance andimprove apparatus uptime

[0111] Far higher MTBF and lower MTTR compared with TWT

[0112] Better gain curve flatness compared with TWT

[0113] Lower noise compared with TWT

[0114] The amplifying means 29 can comprise a signal amplifier 29 and apower amplifier 30, as shown in FIG. 2. The signal amplifier 29 is asemiconductor-based device being adapted to amplify the signal from thesignal generator. The gain of the amplifying means is adjustable byvarying the level of a control signal. Thus the amplitude of the outputcan be selected by the operator.

[0115] The power amplifier 30 is provided for further amplifying thesignal from the signal amplifier. The power amplifier is also asemiconductor-based device with an adjustable gain. The gain is variedby varying the level of a control signal.

[0116] The heating power applied to the applicator is preferably in therange of 1-2000 W depending on the sample size and the chemical reactionin question. Typical ranges are 1-300 W such as 5-50 W, 10-1000 W suchas 30-100 W, and 50-2000 W such as 100-1000 W.

[0117] The necessary power of an electromagnetic radiation used formonitoring or “scanning” (see below) is typically only a fraction of thepower needed for heating. Typical ranges are 0.05100 W such as 0.1-10W.The time of application also varies depending on the sample, process andthe chemical reaction in question. Typical reaction times are 0.1 sec to2 hours such as 0.2-500 sec or 0.5-100 sec.

[0118] The amplified signal from the amplifying means is distributed toone or more applicators using a distributing network.

[0119] The distributing network can comprise many features. FIG. 2 showsan embodiment of the apparatus comprising a selection of these features.FIG. 2 is only an example illustrating how the different features can beimplemented, and the order of the features in FIG. 2 is not restrictive.The following features can be comprised in the distributing network:

[0120] circulators 31

[0121] bi-directional couplers 32

[0122] power meters 34-38

[0123] artificial loads 33

[0124] dividers 51

[0125] combiners 50

[0126] spectrum analysers

[0127] Some of these features will be described in the following withreference to FIG. 2.

[0128] The circulator 31 prevents the reflected power from the microwaveapplicator 24 and the distribution network 23 from entering the poweramplifier 30. Instead the reflected power is directed to a dummy load 33optionally connected to a first power meter 34. Some semiconductor basergenerators and amplifiers, e.g. Silicon-carbide generators/amplifiers,are not affected by backscattered microwaves, and the circulator 31 isnot necessary when such generators/amplifiers are utilised.

[0129] The circulator 31 is adapted to be operationally connectedbetween the amplifying means and the distributing network, and has atleast one input terminal, an output terminal and at least one combinedinput/output terminal. The input terminal is operationally connected tothe output terminal of the amplifying means and the combinedinput/output terminal is operationally connected to the distributionnetwork. Furthermore, the load 33 and first power meter 34 can beincorporated in the apparatus in connection with the circulator.

[0130] The distributing network can comprise a coupler, such as abidirectional coupler 32, said coupler comprising an input terminal, atleast two output terminals and a combined input/output terminal. Theinput terminal can be operationally connected to the output terminal ofthe circulator or amplifier and the output terminal is operationallyconnected to other parts of the distributing network.

[0131] The bi-directional coupler directs a fraction of the input and/orthe reflected power to two power meters 35 and 36. The third power meter36 measures a portion of the power transmitted in the direction towardsthe applicator(s), whereas the second power meter 35 measures a portionof the power transmitted in the opposite direction, i.e. away from theapplicator(s). The power determining means can provide signals to thecontroller 45.

[0132] The distribution network can also comprise combiners 50 anddividers 51 in order to facilitate parallel processing. These caninclude switches so that the structure of the network can be varied.

[0133] In general, the distribution network is provided for distributingthe electromagnetic radiation generated and amplified using thesemiconductor signal generator and the semiconductor amplifiersrespectively. The generated and amplified signal can be distributed to asingle or to a plurality of applicators.

[0134] An example of such a network is coaxial cables with dividers inorder to split up the power/signal line in as many power/signal lines asneeded to feed all the separate applicators. Alternative ways ofaccomplish a distributing network is to use wave-guides, strip-linesetc. The distributing network can be an integral part of the applicatordesign as will be showed in FIGS. 3, 4, 5 and 6.

[0135] Applicators such as 24 can be of various types. According to thepresent invention some features are preferably comprised in theapplicator. Some of these preferred features will be described in thefollowing with reference to FIG. 2. A more detailed description of anumber of embodied applicators will be given later.

[0136] The minimum requirements of an applicator are:

[0137] a) an input terminal 12,

[0138] b) a sample holder 1, and

[0139] c) means for confining the microwave energy from to the inputterminal 12.

[0140] In order to control the operation of the signal generator andamplifier in response to the power absorbed in the sample (or reflectedby the applicator), some measure of the total power absorbed in—andreflected by—the applicator has to be obtained.

[0141] In order to determine the absorbed amount of power (or energy) inthe sample, the applicator can comprise means for determining theelectromagnetic field strength. The applicator can comprise an outputterminal operationally connected to a load 33 that absorbs the reflectedpower from the applicator. Furthermore, fourth power measuring means 37are operationally connected to the load 33 and the control means 45.Also, a loop antenna 13 can act as microwave receiving means. The loopantenna is connected to a fifth power measuring means 38 and the controlmeans 45.

[0142] The above mentioned load 33 and loop antenna 13 are used formonitoring and receiving the microwaves transmitted through the sample 1by transferring the energy to power meters 37 or 38. The differencebetween the power irradiated at the sample and the powertransmitted/reflected by the sample, measured with respective powermeters depending on the exact setup, indicates the sum of the energylosses in the system and energy absorbed in the sample. The applicatorcan be calibrated by measuring the system losses of the unloadedapplicator before the sample is introduced into the applicator. Theenergy absorbed in the sample will characterise the sample in terms ofdielectric properties at a given temperature and frequency. By scanningthe frequency within a given range, e.g. 1-4 GHz, and monitoring thesignals from the load 33 or receiving antenna 13 together with thereflected signal from 35, it will be possible to follow the progress ofa chemical reaction.

[0143] The applicator can also include sensors operationally connectedto the controller in order to monitor and control the application ofmicrowave energy to the sample or samples. Sensors for measuring anyparameter characterising the extent of the process or reaction, such aspressure, temperature, pH, and conductivity, during the heating (and anyintermediate non-heating phases thereof) can be comprised. One possibletemperature sensor for microwave cavities is described in WO 94/24532.The output from such sensors can also provide a measure of the amount ofpower absorbed in the sample.

[0144] Spectrum analysers can be connected to the power measuring means,and the power measuring means can be frequency selective. If theelectromagnetic signal directed to the applicator is time dependent,e.g. pulsed, analysis of the time and frequency spectra of a pulseirradiated at the sample, and the reflected/transmitted signal, canyield valuable information of the sample. This analysis can compriseFourier transformation of the measured signals. This feature is notspecifically connected to the applicator, rather it is a combination ofmeasurements from power meters at different locations in the system,together with analysing means which can be comprised in the controller.

[0145] The applicator is preferably adjustable so that it can be tunedto support modes depending on the used frequency. It should be notedthat the applicator can have a quasistatic, near field, surface field,single mode cavity or multi mode cavity, as well as an open endedcavity. The applicator can be tuned to make its resonance frequencycorrespond to the frequency of the signal connected to the inputterminal 12, e.g. by adjusting certain geometrical parameters, such as aresonator rod, of it.

[0146] The sample 1 can be placed directly in the applicator, but thesample is typically placed in an open or closed sample holder 2. Suchsample holder could be an integral part of the applicator or a separatereaction vessel of any material suitable for use in microwave heatingapplications. As will be known to the person skilled in the art, thematerial constituting the sample holder should preferably not absorb themicrowave energy. Various types of polymers and glasses can be used.Specifically, various types of trays, microtiter plates, etc. canpreferably be used when a plurality of samples is heated simultaneously.A plurality of sample holders can be assembled in a sample holder set,such set-up can generate a very even heating of all samplessimultaneously.

[0147] The sample holder can furthermore be provided with sample inletand outlet ports for sample transfer in and out of the applicator andthe sample holder during or between the process steps or wholeprocesses.

[0148] The free space in the applicator can be filled with an inert gasin order to avoid reaction between gasses and the sample. It is howeverpreferred that the sample holder include a lid. It is preferred that theapplicator includes at least one inlet/outlet for providing an inertatmosphere to the space above the sample. Alternatively, the space abovethe sample is filled with a reactive gas, e.g. H₂, which is useful inhydrogenation reactions.

[0149] The applicator should preferably be able to sustain high internalpressure either formed by the chemical reaction or formed intentionallyto create a high-pressure atmosphere as a reaction parameter. Highinternal pressure is normally used as a method to increase thetemperature of the sample over the boiling point for the liquid phase.The pressure can be kept at a predetermined level or pre-set as a levelnot to be exceeded or fall below. A pressure system incorporates asafety valve function for protection of the pressurised components andpersonal safety.

[0150] Rapid cooling of samples can be a very practical feature, whichcan be comprised in the applicator. Normally, when cooling sampleswithout any use of means for cooling, the time for the sample to reachambient temperature is usually quite long, leading to undesired sidereactions and other unwanted phenomena. A forced cooling can thereforebe used to minimise the time it takes for the sample to reach apredetermined temperature. The cooling device can be of any sort e.g.circulating air, circulating water or other liquid cooling media,peltier elements, etc. The cooling device can also be used to controlthe temperature during the process cycle. One important application ofthe cooling device is where temperature cycling of the sample isdesirable. A pre-programmed temperature cycle is used to control theheating of the sample with microwaves and cooling of the sample by usingthe cooling device. An example of such an application is temperaturecycling to perform the PCR reaction (Polymerase Chain Reaction).

[0151] The controller 45 has a central function as shown in FIG. 2. Thecontrolling device is a computer based system for controlling (run-timecontrol) and programming of the apparatus and all itsmodules/components.

[0152] The controller 45 might be connected to one or several PCs in anetwork as a user interface and/or computing device for one or severalmicrowave apparatuses. In this way storage means for storing data and/orprocessed data and/or data concerning predetermined process parametersbecome available.

[0153] The control signal provided to the generating means 28 by thecontroller 45 varies according to a first function of the back-reflectedor transmitted signal from the applicator 24, said back-reflected ortransmitted signal being detected by one of the power measuring means34-38. The control signal provided to the amplifying means 29 and 30 bythe controller varies according to a second function of theback-reflected or transmitted signal from the applicator, saidback-reflected or transmitted signal being detected by one of the powermeasuring means 34-38.

[0154] The control signal provided to the generating means 28 determinesthe output frequency, the control signal provided to the amplificationmeans 29 and 30 determines the amplitude of the amplified signal. Theamplitude of the amplified signal can be varied as a function of time.

[0155] The control system has three different modes of operation:

[0156] 1) heating mode

[0157] 2) monitoring mode

[0158] 3) programming mode

[0159] Operating the controller 45 in heating mode puts specificrequirements to the configuration of the controller. The controller iscapable of setting and controlling the output power from the signalamplifier 29 and the power amplifier 30. Furthermore, the controller iscapable of modulating the signal generated by the signal generator 28 soas to generate an output signal, which is a function of time such as arectangular or triangular wave form. In the same context, the dutycircle of the signal must be adjustable so as to reduce the power of thedelivered signal.

[0160] The above-mentioned feature is provided by applying a firstcontrol signal to the signal amplifier 29 and a second control signal tothe power amplifier 30.

[0161] Another feature, which has to be incorporated in the controller,is the ability to control the output frequency of the signal generator.Also the settings relating to frequency scans, i.e.

[0162] start frequency, stop frequency, frequency resolution and scantime must be controllable from the controller. The starting frequency isin the range of 0.5-300 GHz, preferably in the range of 1-30 GHz.Predetermined values between which the frequency of the electromagneticradiation is varied are in the range of 0.5-300 GHz, preferably in therange of 1-30 GHz.

[0163] Furthermore, the process time for a complete process or parts ofa process if it involves more than one step should be controllable.

[0164] Measuring the input power to the applicator by means of a powermeter 36 is accomplished, however, the optimal position of power meter36 depends on the exact configuration of the distributing network.Likewise, the reflected power from the applicator is measured with powermeters 34 or 35 whereas 37 or 38 measures the power coupled out from theapplicator. The power absorbed in the applicator can be measured bycalibrating the apparatus with an empty cavity to measure the losses inthe applicator. This calibration can be done within the frequency rangewhere the sample is to be processed. By subtracting the reflected powerand the loss power of an empty applicator the absorbed power can becalculated.

[0165] The power signal measured by the power meters 34 to 38 aretransmitted to the controller so as to be used for controlling thefrequency of the signal generator 28 and/or the gain in the signalamplifier 29 and/or the power amplifier 30.

[0166] The controller 45 can also provide control signals for systemcomponents—such as directional couplers 32, circulators 31, etc. Thecontroller can provide other types of signal processing. The controllercan control and monitor sample parameters such as temperature, pressure,pH, conductivity, etc, using the previously mentioned sensors. Bycurrent measuring of such parameters, the controller can respond if aparameter reach a predetermined values. It is possible to set a maximumvalue not to be exceeded during the process and a minimum value not tofall below during the process.

[0167] Determining the coupling between the electromagnetic radiationand the sample and varying the frequency and power of the radiation isessential. Furthermore, the frequency of the electromagnetic radiationcan be changed in response to a change of the level of the feedbacksignal by more than a predetermined threshold value. Data concerning thefrequency and the coupling efficiency—measured as a reflectionfactor—between the electromagnetic radiation and sample 1, can be storedin a memory for further processing.

[0168] In the monitoring mode, a scan function is available thatnormalises the signal from a first scan (gives a strait baseline), anddetects the difference from the normalised baseline during a number ofsubsequent scanning cycles. Tracking and locking to the frequency thatgives maximum power absorbed in the sample 1, (moving maxima) is anotheravailable feature. The frequency of the microwave generator 28 isadjustable to an extent of at least±30% around a centre frequency.

[0169] When the apparatus operates in programming mode the possibilityof creating, storing, retrieving and editing using an in-built highlevel method programming language must be available for the operator. Amethod is a pre-programmed sequence of events where every event has atleast one process as input. A process parameter is e.g. power, timepressure etc.

[0170] The apparatus can also comprise means of collecting andprocessing all process data and store and/or retrieve said data from aninternal and/or external database.

[0171] By using an apparatus with said monitoring and controlling meanscombined with at least one of the following parameters to be variable:frequency, waveform, power, time, temperature, pressure, artificialatmosphere, it is possible to optimise and maintain these optimalconditions for said chemical reaction.

[0172] Referring again to FIG. 2, an apparatus for microwave assistedchemical and biological reactions is illustrated. One of the mainfeatures of the apparatus aims at optimising the reaction conditions forsaid chemical reaction. Another set of features of the apparatus aims atmonitoring and controlling the optimised conditions for said chemicalreaction. Yet another set of features aiming at process data collection,data processing, storing and retrieving data from an internal and/or anexternal database.

[0173] When two or more starting materials reacts chemically they aresubject to changes in their physical and chemical properties. Thesechanges in properties are usually temperature dependent. Chemicalreactions are often performed at elevated temperature to enhance thespeed of the reaction or supply enough energy to initiate and maintain areaction. The form of the supplied energy could be thermal radiation,ultrasound, microwaves etc. In the case of microwaves as supplied formof energy the transferred energy into the reacting materials isdependent of the dielectric properties of the starting and formedmaterials during the chemical reaction. The dielectric properties aretemperature dependent and will therefore vary during the chemicalprocess. Changes in dielectric properties will also take place due toforming of new materials in the chemical reaction. The dielectricproperties of materials are also known to change with the frequency.

[0174] In an apparatus with frequency tuning, an optimum of coupledenergy into the reaction will occur at a specific frequency. Thisfrequency will change according to the temperature in the reaction inaccordance with the dependence of the samplespermittivity ε′ upontemperature.

[0175] The term “chemical reaction” is intended to mean any inorganicand organic reaction involving the formation or breaking of a (covalent)bond between two atoms, as well as conformer reactions of clusters andlarge molecules. It should be understood that the term also includesreactions where enzymes are involved as catalysts, e.g. the polymerasechain reaction (PCR) and similar types of reactions. The chemicalreaction is preferably a reaction involving organic compounds, i.e. lowmolecular organic compounds and biological organic compounds (e.g.enzymes). It is furthermore preferred that a conversion of the chemicalconstitution of one or more organic compound takes place.

[0176] The chemical reactions are typically organic chemical reactionsof which virtually all known reactions are applicable. Typical reactionstypes are polymerisation/oligomerisation, esterification,decarboxylatio, esterification, hydrogenation, dehydrogenation, additionsuch as 1,3-dipolar addition, oxidation, isomerisation, acylation,alkylation, amidation, arylation, Diels-Alder reactions such asmaleinisation and fumarisation, epoxidation, formylation,hydrocarboxylation, hydroboration, halogenation, hydroxylation,hydrometallation, reduction, sulphonation, aminomethylation, ozonolysis,etc. It is believed that the apparatus and methods according to theinvention are especially suited for reactions involving one or morecatalysts and for asymmetric organic reactions.

[0177] The chemical reaction can take place in a suitable solvent or inneat form. When a solvent is used, it is preferred that the dissipationfactor (or loss tangent) is greater than about 0.04 at room temperature.Examples of suitable solvents are acetonitrile, DMF, DMSO, NMP, water,tert-butanol, EtOH, benzonitrile, ethylene glycol, acetone, THF. Thefrequency of the generated electromagnetic signal can be tuned toabsorption bands/peaks for the used solvent.

[0178] The chemical reactions typically involve a starting material(substrate or “chemical species”), a reagent and optionally a catalyst(e.g. an enzyme such as a thermostable DNA polymerase). The startingmaterial can be any chemical substance in any phase, solid phase, liquidphase or gas phase. Included in starting materials are all materialsused for e.g. solid support of reactants in chemical reactions. Startingmaterials also includes all materials (chemical substances) formed underthe chemical reaction and can be considered as new starting material fora subsequent chemical reaction during the same process or in a newprocess performed in the same apparatus. Staring material or reagentscan also be included in the gas phase of an artificial atmosphere. Thefinished chemical product from a previous chemical reaction, performedin the apparatus, shall also be considered as starting material for asubsequent chemical reaction performed in the apparatus.

[0179] The applicator 24 comprises a cavity or cavities for applyingmicrowave energy to one or more samples 1. It should be understood thatthe various types of cavities and arrangements of cavities representdifferent embodiments of the applicator in the apparatus according tothe present invention. As the apparatus in principle may involve anapplicator of any known type (although with different degrees ofsuccess), the present invention is not limited to the specificallymentioned variants. In the following, different embodiments showingdifferent applicator designs and degree of parallel processing isdescribed. These embodiments may serve as applicator 24 in relation toFIGS. 1 and 2.

[0180]FIG. 3 illustrates a number of cavities mounted in an array. Thisarray can be, but is not limited to, a microtiter plate 4. Each cavityis defined by a lid 6, a bottom plate 8 and an outer metal tube 17. Eachcavity comprises a sample holder 2, a resonator rod 16 for adjusting theresonance frequency of the cavity, input and output signal loopantennas18, and optionally a gas inlet/outlet 15. The microwaves areintroduced inductively through loop antennas18 as showed in FIG. 3,alternatively they can be introduced capacitative via a distributingnetwork feeding the whole array. The sample is placed on the resonatorrod 16 in the outer tube 17 of the cavity. The length of the resonatorrod can be adjusted for changing the resonance frequency of the cavity.All components are electrical connected to each other to form a closedelectrical circuit. The cavity could be pressurised and put under anartificial atmosphere.

[0181] Another application is illustrated in FIG. 4A and B where foursample wells 9 are assembled symmetrical in a sample holder set. Ashielding metal cage 3 serving as walls in a cavity surrounds the foursample holders. The microwave transmitting device 5 is placed in thecentre of the space defined between the four individual sample holdersand thereby irradiates the four samples 1 simultaneously. Thus, in theembodiment illustrated in FIG. 4, a number (4 in the example) of samplesare processed in parallel. As illustrated in FIG. 4B, a plurality ofcavities can be arranged in an array similar to the array described inrelation to FIG. 3.

[0182]FIG. 5 illustrates a configuration where the transmitting orreceiving devices, 12 or 13 respectively, are mounted on thebottom-plate 8, and where these devices form an array. The lid 6 ismounted on top of the plate, and the receiving or transmitting device,13 or 12, can be mounted on the lid. The bottom-plate or the lid can be,but is not limited to, a microtiter plate. The bottom-plate 8 and thelid 6 define a cavity with a metal tube 3. A vial made of a suitablematerial (glass or a polymer, e.g. polystyrene) is inserted into themetal tube to serve as a sample holder 2. A cooling device can beattached at the bottom-plate. In order to dissipate the microwave energynot absorbed, the lid can include a microwave absorbing material Thecooling device can also be attached to the lid in order to take care ofthe dissipated energy. An inlet/outlet port 15 for artificial atmospherecan be attached to the lid and/or the bottom-plate. The reaction vesselcan be pressurised by using the artificial atmosphere or internallygenerated pressure from the chemical reaction. Field confinement can beachieved by using a high permittivity body at 12 or 13. Thereby the lidcan be removed and the applicator becomes an open-end applicator.

[0183]FIG. 6 illustrates a microtiter plate with an individual antenna 5for each sample well, where the antenna is immersed in the sample well.Sample wells are arranged in an array and a metal tube 3 surrounds eachwell as a shield. A glass or plastic sample holder 2 is typicallyinserted into the metal tube 3 to serve as a sample holder. As in thecase of the embodiments of FIGS. 3 and 5, each sample is processedindividually.

[0184] General guidelines and instructions for the work with microwavesand the constructions of microwave cavities are, e.g., given in Gabriel,et al., Chem. Soc. Rev, 1998, Vol. 27, pp 213-223 and in MicrowaveEngineering, Harvey (ed.), Academic Press, London 1963 (in particularChapters 4-6).

[0185] The apparatus according to the invention is suited for heating atleast one reaction mixture (sample) comprising at least one organiccompound. The reaction mixture or each of the reaction mixtures(samples) can further comprise one or more reagents and optionally acatalyst (e.g. an enzyme).

[0186] In a particularly interesting embodiment, the apparatus isadapted for heating two or more reaction mixtures simultaneously orsequentially or intermittently.

[0187] In one important embodiment of the present invention, a pluralityof chemical reactions are performed in parallel. This is realistic dueto the cost efficient construction of the apparatus according to theinvention. FIG. 1 illustrates the principles behind the parallelprocessing of a plurality of samples.

[0188] The present invention also provides a method of performing aplurality of chemical reactions simultaneously or sequentially,according to the third aspect of the present invention describedearlier.

[0189] This and the following methods are all suitable performed byusing the apparatus defined herein.

[0190] The fact that the electromagnetic radiation can be adapted toeach sample (e.g. with respect to frequency, heating time, power,pulsing of the signal, signal cycles, etc.) is important, e.g. inoptimising processes and in the construction of libraries of chemicalcompounds. In the latter case, any differences in reactivity within thevarious reagents and various substrates (and enzymes) can be compensatedfor by the apparatus. Thus, in a further embodiment of the presentinvention, the apparatus is used for preparing a combinatorial libraryof compounds (at least 4 compounds). Also, the apparatus and the methodaccording to the invention can be used to prepare a large number ofcompounds in a parallel process, where the compounds are not part ofcombinatorial library, i.e. where the compounds do not share commonstructural features. This is possible in a parallel process since theapparatus is capable of coupling the application of the electromagneticradiation to each sample independently. A further interesting variant isthe continuous preparation of compounds by using a sample holder havinga sample inlet and a sample outlet. In this latter situation, a samplecan be introduced in a sample holder formed as a loop or spiral of atube, a rinsing solution is subsequently introduced through the sampleinlet thereby forcing the sample out of the sample holder through thesample outlet, and a new sample is subsequently introduced. Due to therelatively short reaction time under microwave heating conditions, alarge number of samples can be processed in parallel (several sampleholders) or sequentially (one sample holder).

[0191] The process parameters, i.e. with respect to the frequency andthe power of the electromagnetic radiation, are controlled by thecontroller (45). As should be understood from the above, theelectromagnetic radiation is preferably provided by a semiconductorbased signal generator, in particular by an apparatus as defined in thefirst aspect of the present invention. In certain applications, e.g.where a heating/cooling cycle is required, the electromagnetic radiationis preferably applied intermittently. Alternatively, any cooling meanscan be activated intermittently.

[0192] As mentioned above, the electromagnetic radiation is adaptedspecifically to each of the samples, i.e. for each sample/sample holderthe process parameters are independently selected. This means that eachof the samples are processed under different conditions, or that sets ofsamples are treated under substantially identical conditions butconditions different from other sets of samples, or that all samples aretreated under substantially identical conditions. In the event that aset of samples is treated under substantially identical conditions, itcan be advantageous to use an applicator essentially as illustrated inFIG. 4, where the sample holders are collected in sets consisting of twoor more sample holders (a set of four sample holders is shown in FIG.4). Such sample holder sets typically consist of 2-1000 sample holders,typically from 3-96 sample holders.

[0193] The apparatus will be able to generate data as an expression ofthe progress and completion of a chemical reaction. Such data can bestored in a database operationally associated with the controller.Furthermore the database might be provided with information regardingthe product arising from the chemical reaction, e.g. purity,enantiomeric purity, yield, etc. In the event that a plurality ofreaction mixtures are heated simultaneously in separate cavities underdifferent conditions (e.g. conditions with respect to frequency, heatingtime, heating cycles, heating power, concentration of reagent, substrateand any catalyst, signal shape, reflected power, transmitted power,temperature, pressure, artificial atmosphere, type of sample vial, etc)or subsequently in the same or separate cavities under differentconditions, such data will after proper analysis (e.g. automatedstatistical analysis) provide a unique possibility of optimising thereaction condition for subsequent similar chemical reactions. Theprocessed data can be analysed with a suitable analysing method andevaluated to find optimal parameter settings and conditions. The resultfrom the process can be processed by multivariant data analysis foroptimisation.

[0194] Furthermore it will be possible to provide a set of suitablereaction conditions for subsequent reactions of the same type, e.g.substitution reactions using a specific class of catalysts, Diels-Alderreactions using specific substrates, etc.

[0195] In a further prospect of the present invention, it is envisagedthat such data for optimal (or suitable) process parameters for a numberof standard type reactions can be identified by the supplier of theapparatus and be provided together with the apparatus according to theinvention. Thus, in a preferred embodiment, the storage means associatedwith the controller includes a section designated for predeterminedprocess parameters. Such a section could be formed as a replaceablememory card (or a “Smart Card”) which can be updated regularly by thesupplier of the apparatus and provided to the user of the apparatus.

[0196] Consequently, the present invention also relates to a method andthe use as above wherein the frequency of the electromagnetic radiationsupplied to the sample in the applicator, the level of transmitted powerand the period of application of the electromagnetic radiation isdetermined by pre-set values for the chemical reaction in question, suchpre-set values being stored in a storage means associated with thecontroller of the apparatus.

[0197] Thus, a further interesting aspect previously described as theninth aspect, the present invention is a kit for chemically reacting achemical species with a reagent optionally under the action of acatalyst, where the chemical reaction is performed in an apparatus asdefined in the first aspect of the present invention.

[0198] In the ninth aspect, it should be understood that the sampleholder provided with the kitcan comprise one or more necessary reagentsand/or any suitable catalyst so that the user only needs to provide thechemical species to the sample holder. The solvent (if a solvent isnecessary or desirable) is preferably also provided with the kit so asto ensure that the reagent and catalyst will become fullydissolved/dispersed. Alternatively, the sample holder can contain thereagent and/or the catalyst in immobilised form so as to facilitate theisolation of the product of the chemical reactions.

[0199] The apparatus makes it possible to perform a number of othervaluable methods for performing chemical reactions. In one embodiment,the progress of the reaction is simultaneously monitored by scanning thesample before (reference set of reflection factors) and afterapplication of the electromagnetic radiation. By comparing a set ofreflection factors after and before (reference set) heating, theprogress can be determined. Comparison of microwave signals between areference situation (empty applicator) and a situation where a sample isintroduces in an applicator is described in U.S. Pat. No. 5,521,360. Inrespect of the present invention, it is possible vary the processparameters by means of the controller (45) in response to the measuredsets of reflection factors. The sets of coupling efficiencies canpreferably be normalised and/or transposed before comparison.

[0200] Thus, the present invention provides a method for performing achemical reaction according to the third aspect of the present inventiondescribed earlier.

[0201] In one intriguing variant (the “biosensor” variant) of the abovemethod, the first (reference) varying of the frequency (step (b)) (a“scan”) is performed prior to introduction of chemical substance to thesample. The sample can comprise an enzyme or a biomolecule or a cell,for which the chemical substance is a substrate or a ligand. Thesubsequent “scan” is then performed and the difference in reflectionfactor is expected to reflect the interaction between the chemicalsubstance and the components of the sample. This embodiment can be anespecially interesting variant for studying the interaction between aligand/substrate and an enzyme. The heating (step (c)) is often omittedin this variant. Furthermore, repeating the steps will only be necessaryin order to study the mentioned interaction over time, otherwise onlycomparison of two sets of reflection factors will be necessary.

[0202] Furthermore, the present invention also provides a method foridentifying minimum reflection (or two or more minima) for applicationof electromagnetic radiation (especially where the predetermined rangecomprises the frequency that provides optimal coupling between theelectromagnetic radiation and the sample). I.e. the present inventionprovides a method of performing a chemical reaction according to thefifth aspect of the present invention described earlier.

[0203] The invention also provides a method for seeking for a frequencyrepresenting a local (or global) reflection factor while performing achemical reaction, i.e. a method of performing a chemical reactionaccording to the sixth aspect of the present invention describedearlier.

[0204] The invention furthermore provides a method for seeking for afrequency where the reflection factor has a predetermined level whileperforming a chemical reaction, i.e. a method of performing a chemicalreaction according to the seventh aspect of the present inventiondescribed earlier.

[0205] In an especially interesting variant of the methods describedherein, each sample comprises at least one enzyme and, further, eachsample is a PCR mixture.

[0206] The PCR reaction is a particularly interesting application forthe apparatus according to the sixth aspect of the present invention asthe apparatus provides means for varying and pulsing the energy applied(and thereby the temperature of a PCR vial) accurately. Furthermore, theapparatus comprises means for controlling and monitoring the progress ofthe PCR reaction.

[0207] The PCR technique is generally described in U.S. Pat. Nos.4,683,202 and 4,683,196. The use of microwave radiation for heating PCRmixtures is known, i.e. from WO 91/12888, WO 95/15671 and WO 98/06876,however processing by using the apparatus according to the presentinvention provides unprecedented advantages over the known systems.General guidelines for handling and processing PCR mixtures (e.g.temperature ranges and cycle numbers and times) can be found in WO98/06876. A typical example of a temperature cycle for a PCR is adenaturation heating step up to around 80-100° C. (e.g. 0.5-3 minutes),a cooling step where the mixture is brought to around 20-40° C. (e.g.0.1 to 1 minute) and a polymerisation step at around 55-75° C. (e.g. for1-5 minutes). A complete amplification reaction typically involves15-100 cycles, e.g. around 25-35 cycles.

[0208] With the present invention, it is possible to control theapplication of energy very accurately and to apply the energy incontrollable doses and to cool the samples very rapidly so as to reducethe cooling steps. Furthermore, it is also possible to monitor theprogress of the reactions by applying a low intensity microwave signalto the reaction mixture, e.g., in each cooling step so as to determinethe completion (relative to certain criteria) of the reactions. Thus,the electromagnetic radiation is preferably applied in cycles of atleast two levels where the samples are cooled at least during a part ofeach cycle. The at least two levels can represent the temperature levelsof 80-100° C. and 55-75° C. Typically, the cooling is initiated in orderto reach a temperature level of 20-40° C. The cooling can also beapplied constantly (e.g. in the form of a cold block (bottom plate) inorder to obtain a steeper cooling gradient.

1. An apparatus for providing electromagnetic radiation to a firstapplicator, said apparatus comprising: a) a first generating means forgenerating electromagnetic radiation, b) a first amplifying means foramplifying the generated electromagnetic radiation, c) means for guidingthe amplified electromagnetic radiation to the first applicator, and d)means for controlling the first generating means and the firstamplifying means, wherein the generated electromagnetic radiationcomprises a plurality of frequencies, and wherein the first generatingmeans and the first amplifying means are essentially constituted bysemiconductor components.
 2. An apparatus according to claim 1 furthercomprising a second applicator.
 3. An apparatus according to claim 2,wherein the guiding means further comprises means for guiding at leastpart of the amplified electromagnetic radiation to the secondapplicator.
 4. An apparatus according to any of claims 1-3 furthercomprising a second generating means for generating electromagneticradiation at a plurality of frequencies and a second amplifying meansfor amplifying the electromagnetic radiation generated by the secondgenerating means.
 5. An apparatus according to claim 4, wherein thesecond generating means and the second amplifying means are essentiallyconstituted by semiconductor components
 6. An apparatus according toclaim 5 further comprising guiding means for guiding the electromagneticradiation amplified by the second amplifying means to the secondapplicator.
 7. An apparatus according to claim 6, wherein the guidingmeans further comprises means for guiding at least part of theelectromagnetic radiation amplified by the second amplifying means tothe first applicator, and second applicator, and wherein the guidingmeans comprises means for switching the electromagnetic radiationamplified by the second amplifying means between the first and secondapplicator.
 9. An apparatus according to any of the preceding claims,wherein the first and second applicators are selected from the groupconsisting of near field, surface field, single mode and multi modeapplicators.
 10. An apparatus according to any of the preceding claims,wherein the semiconductor components constituting the first and secondamplifying means comprise silicon-carbide power transistors.
 11. Anapparatus according to any of claims 4-10, wherein the frequency of theelectromagnetic radiation generated by the first and second generatingmeans varies according to a first and second control signal,respectively, said first end second control signal being provided by thecontrol means.
 12. An apparatus according to any of claims 4-11, whereinthe amplification of the first and second amplifying means variesaccording to a first and second control signal, respectively, said firstand second control signal being provided by the control means.
 13. Anapparatus according to claim 11, wherein the frequency of theelectromagnetic radiation generated by the first and second generatingmeans is within the range 300 MHz-300 GHz, such as within the range0.5-3 GHz or within the range 50-100 GHz.
 14. An apparatus according toany of the preceding claims, wherein the control means comprises ageneral purpose computer.
 15. A method for performing a plurality ofchemical reactions simultaneously or sequentially, said methodcomprising the steps of: a) providing a first sample into a firstapplicator, b) providing a second sample into a second applicator, andc) applying electromagnetic radiation to the first and second samplessimultaneously or sequentially for a predetermined period of time, saidelectromagnetic radiation having a frequency in the range of 300 MHz-300GHz.
 16. A method according to claim 15, wherein the electromagneticradiation is provided specifically and independently to each of thesamples.
 17. A method according to claim 15 or 16, wherein the appliedelectromagnetic radiation comprises one or more pulses.
 18. A methodaccording to any of claims 15-17, wherein each sample is a PCR mixture.19. A method according to any of claims 15-18, wherein theelectromagnetic radiation is applied in cycles of at least two stepswhere the samples are cooled at least during a part of each cycle.
 20. Amethod according to any of claims 15-19, wherein the electromagneticradiation is provided by an apparatus according to any of claims 1-14.21. A method for performing a chemical reaction, said method comprisingthe steps of: a) providing a sample in an applicator, b) applyingelectromagnetic radiation to the sample for a first predetermined periodof time at a first level of power and varying the frequency of theelectromagnetic radiation between two predetermined values and with apredetermined resolution, and determining a reflection factor ofelectromagnetic radiation from the sample at at least some (two) of thefrequencies covered by the range of the two predetermined values bydetermining the level of a feed-back signal, thereby obtaining a firstset of reflection factors, c) changing the physical and/or chemicalproperties of the sample, d) applying electromagnetic radiation to theapplicator at a second level of power and varying the frequency of theelectromagnetic radiation between two predetermined values and with apredetermined resolution, the range defined by the predetermined valuesbeing included in the range defined by the predetermined values in stepb), and determining a reflection factor of electromagnetic radiationfrom the sample at at least some (two) of the frequencies covered by therange of the two predetermined values by determining the level of thefeed-back signal, thereby obtaining a second set of reflection factors,and e) repeating step c) and d) until the difference in reflectionfactors calculated as the mathematical difference (subtraction) betweenthe frequencies associated with the first and second set of reflectionfactors is within a predetermined range.
 22. A method for performing achemical reaction, said method comprising the steps of: a) providing asample in an applicator, b) applying electromagnetic radiation to thesample, the electromagnetic radiation having a starting frequency, c)varying the frequency of the applied electromagnetic radiation betweentwo predetermined values and with a predetermined resolution, d)determining a reflection factor of electromagnetic radiation from thesample by determining a level of a feed-back signal during at least partof the varying of the frequency of the electromagnetic radiation, and e)determining, from the level of the feed-back signal, the frequency ofthe electromagnetic radiation where the reflection factor is within apredetermined range.
 23. A method for performing a chemical reaction,said method comprising the steps of: a) providing a sample in anapplicator, b) applying electromagnetic radiation to the sample, theelectromagnetic radiation having a starting frequency, c) varying thefrequency of the electromagnetic radiation incrementally around thestarting frequency, d) determining a reflection factor ofelectromagnetic radiation from the sample by determining a level of afeed-back signal at the starting frequency, at a frequency incrementallylower than the starting frequency and at a frequency incrementallyhigher than the starting frequency, e) repeating step b) to d) until thereflection factor is minimum.
 24. A method for performing a chemicalreaction, said method comprising the steps of: a) providing a sample inan applicator, b) applying electromagnetic radiation to the sample, theelectromagnetic radiation having a starting frequency, c) varying thefrequency of the electromagnetic radiation incrementally around thestarting frequency, d) determining a reflection factor ofelectromagnetic radiation from the sample by determining a level of afeed-back signal at the starting frequency, at a frequency incrementallylower than the starting frequency and a frequency incrementally higherthan the starting frequency, e) comparing the determined reflectionfactor with a predetermined reflection factor, f) adjusting the startingfrequency to a frequency so that the determined reflection factor iswithin a predetermined range around the predetermined reflection factor,and g) repeating step c) to f) as often as desirable.
 25. A methodaccording to any of claims 21-24, wherein the starting frequency is inthe range of 300 MHz-300 GHz.
 26. A method according to any of claims21-25, wherein the predetermined values between which the frequency ofthe electromagnetic field is varied are in the range of 300 MHz-300 GHz,such as within the range 0.5-3 GHz or within the range 50-100 GHz.
 27. Amethod according to any of claims 21-26, wherein the reaction isconducted in an apparatus according to any of claims 1-14.
 28. A methodfor performing a chemical reaction, said method comprising the steps of:a) providing a sample in an applicator, b) applying electromagneticradiation to the sample in form of a first pulse with a predeterminedshape and characterising a reflected pulse from the applicator byperforming a mathematical operation so as to obtain a first reflectedspectrum, c) changing the physical and/or chemical properties of thesample, d) applying electromagnetic radiation to the sample in form of asecond pulse with a predetermined shape and characterising a reflectedpulse from the applicator by performing a mathematical operation so asto obtain a second reflected spectrum, e) repeating step c) and d) untilthe difference between the first and second reflected spectra calculatedas the mathematical difference (subtraction) between the first andsecond spectra is within a predetermined range.
 29. A method accordingto claim 28, wherein the mathematical operation for obtaining the firstand second reflection spectra comprise Fourier Transformation.
 30. Amethod according to claim 28 or 29, wherein the reaction is conducted inan apparatus according to any of claims 1-14.
 31. The use of anapparatus according to any of claims 1-14 for temperature cycling a PCRmixture.
 32. The use according to claim 31 for performing a chemicalreaction in a sample, wherein the frequency of the electromagneticradiation applied to the sample in the applicator, the level ofirradiated power and the period of applying the electromagneticradiation is determined by pre-set values for the chemical reaction inquestion, such pre-set values being stored in a storage means associatedwith the control means.
 33. The use according to claim 31 or 32, whereincorresponding data of frequency and reflection factor are stored in amemory for further processing.
 34. The use according to claims 33,wherein further processing is performed in a neural network.
 35. A kitfor chemically reacting chemical species with a reagent optionally underthe action of a catalyst, wherein the chemical reaction is performed inan apparatus according to any of claims 114, said kit comprising: a) asample holder comprising at least one of the reagent and the optionalcatalyst, b) an electronic storage means comprising data concerning thechemical reaction between the chemical species and the reagent under theoptional action of the catalyst, said electronic storage means andapparatus being adapted for retrieving the data from the storage meansand processing said data so as to control the application of anelectromagnetic radiation to said sample holder.
 36. A kit forchemically reacting chemical species with a reagent according to claim35, said kit further comprising instructions regarding addition of thechemical species to the sample holder.